Memory element, memory apparatus

ABSTRACT

A memory element including a layered structure including a memory layer having magnetization perpendicular to a film face in which a direction of the magnetization is changed depending on information stored therein, a magnetization-fixed layer having magnetization perpendicular to the film face, which becomes a base of the information stored in the memory layer, and an intermediate layer that is formed of a non-magnetic material and is provided between the memory layer and the magnetization-fixed layer.

RELATED APPLICATION DATA

This application is a reissue of U.S. patent application Ser. No.15/371,863, now U.S. Pat. Ser. No. 9,917,248, that is a continuation ofU.S. patent application Ser. No. 14/358,645 filed May 15, 2014, theentirety of which is incorporated herein by reference to the extentpermitted by law. U.S. patent application Ser. No. 14/358,645 is theSection 371 National Stage of PCT/JP2012/06976 filed Oct. 31, 2012. Thepresent application claims the benefit of priority to Japanese PatentApplication No. JP 2011-261854 filed on Nov. 30, 2011, in the JapanPatent Office, the entirety of which is incorporated by reference hereinto the extent permitted by law.

TECHNICAL FIELD

The present disclosure relates to a memory element and a memoryapparatus that have a plurality of magnetic layers and make a recordusing a spin torque magnetization inversion.

BACKGROUND ART

Along with a rapid development of various information apparatuses frommobile terminals to large capacity servers, further high performanceimprovements such as higher integration, increases in speed, and lowerpower consumption have been pursued in elements such as a memory and alogic configuring this. In particular, a semiconductor non-volatilememory has significantly progressed, and, as a large capacity filememory, a flash memory is spreading at such a rate that hard disk drivesare replaced with the flash memory. Meanwhile, the development of FeRAM(Ferroelectric Random Access Memory), MRAM (Magnetic Random AccessMemory), PCRAM (Phase-Change Random Access Memory), or the like hasprogressed as a substitute for the current NOR flash memory, DRAM or thelike in general use, in order to use them for code storage or as aworking memory. A part of these is already in practical use.

Among them, the MRAM performs the data storage using a magnetizationdirection of a magnetic material, so that high speed and nearlyunlimited (10¹⁵ times or more) rewriting can be made, and therefore hasalready been used in fields such as industrial automation and anairplane. The MRAM is expected to be used for code storage or a workingmemory in the near future due to the high-speed operation andreliability. However, it has challenges related to lowering powerconsumption and increasing capacity actually. This is a basic problemcaused by the recording principle of the MRAM, that is, the method ofinverting the magnetization using a current magnetic field generatedfrom an interconnection.

As a method of solving this problem, a recording method not using thecurrent magnetic field, that is, a magnetization inversion method, isunder review. In particular, research on a spin torque magnetizationinversion has been actively made (see, for example, Patent Documents 1,2, and 3, and Non-Patent Documents 1 and 2).

The memory element using a spin torque magnetization inversion oftenincludes an MTJ (Magnetic Tunnel Junction) element and TMR (TunnelingMagnetoresistive) element, similarly to the MRAM.

This configuration uses a phenomenon in which, when spin-polarizedelectrons passing through a magnetic layer which is fixed in anarbitrary direction enter another free (the direction is not fixed)magnetic layer, a torque (which is also called as a spin transfertorque) is applied to the magnetic layer, and the free magnetic layer isinverted when a current having a predetermined threshold value or moreflows. The rewriting of 0/1 is performed by changing the polarity of thecurrent.

An absolute value of a current for the inversion is 1 mA or less in thecase of an element with a scale of approximately 0.1 μm. In addition,because this current value decreases in proportion to a volume of theelement, scaling is possible. Furthermore, because a word line necessaryfor the generation of a recording current magnetic field in the MRAM isnot necessary, there is an advantage that a cell structure becomessimple.

Hereinafter, the MRAM utilizing a spin torque magnetization inversionwill be referred to as ST-MRAM (Spin Torque-Magnetic Random AccessMemory). The spin torque magnetization inversion is also referred to asspin injection magnetization inversion. Great expectations are placed onthe ST-MRAM as a non-volatile memory capable of realizing lowerpower-consumption and larger capacity while maintaining the advantagesof the MRAM in which high speed and nearly unlimited rewriting may beperformed.

CITATION LIST Patent Document

Patent Document 1: Japanese Unexamined Patent Application Laid-open No.2003-17782

Patent Document 2: U.S. Pat. No. 6,256,223

Patent Document 3: Japanese Unexamined Patent Application Laid-open No.2008-227388

Non-Patent Document

Non-Patent Document 1: Physical Review B, 54, 9353 (1996)

Non-Patent Document 2: Journal of Magnetism and Magnetic Materials, 159,L1(1996)

Non-Patent Document 3: Nature Materials., 5, 210(2006)

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

Although various materials are considered as a ferromagnetic materialused for the memory element of the ST-MRAM, a material having aperpendicular magnetic anisotropy is generally regarded as suitable forlower power-consumption and larger capacity as compared with a materialhaving an in-plane magnetic anisotropy. This is because theperpendicular magnetization has a lower threshold value that should beexceeded during a spin torque magnetization inversion and aperpendicular magnetization film has a high magnetic anisotropy that isadvantageous for holding the thermal stability of the memory elementminiaturized by the increase in capacity.

Meanwhile, in order to realize a memory element with a high density, itis essential to hold a record stably at a low current. However, a memoryelement having a perpendicular magnetic anisotropy generally has beenknown to have a high damping constant that contributes to a recordingcurrent, and therefore are disadvantageous for decreasing the recordingcurrent.

In view of the above, it is an object of the present disclosure topropose a relatively easy method of improving magnetic properties anddecreasing a recording current, and to provide a memory element that iscapable of making a record stably at a low current as the ST-MRAM.

Means for Solving the Problem

A memory element of the present disclosure includes a layered structureincluding a memory layer having magnetization perpendicular to a filmface in which a direction of the magnetization is changed depending oninformation, a magnetization-fixed layer having magnetizationperpendicular to the film face, which becomes a base of the informationstored in the memory layer, and an intermediate layer that is formed ofa non-magnetic material and is provided between the memory layer and themagnetization-fixed layer. Then, the memory layer includes a multilayerstructure layer in which a non-magnetic material and an oxide arelaminated, and the direction of the magnetization of the memory layer ischanged by applying a current in a lamination direction of the layeredstructure to record the information in the memory layer.

Moreover, a memory apparatus of the present disclosure includes a memoryelement that holds information based on a magnetization state of amagnetic material, the memory element including a layered structureincluding a memory layer having magnetization perpendicular to a filmface in which a direction of the magnetization is changed depending oninformation, the direction of the magnetization of the memory layerbeing changed by applying a current in a lamination direction of thelayered structure to record the information in the memory layer, thememory layer including a multilayer structure layer in which anon-magnetic material and an oxide are laminated, a magnetization-fixedlayer having magnetization perpendicular to the film face, which becomesa base of the information stored in the memory layer, and anintermediate layer that is formed of a non-magnetic material and isprovided between the memory layer and the magnetization-fixed layer, andtwo types of interconnections intersecting with each other. Then, thememory layer is disposed between the two types of interconnections, andthe current in the lamination direction is applied to the memory elementthrough the two types of interconnections.

According to the memory element of the present disclosure, because itincludes a memory layer that holds information based on a magnetizationstate of a magnetic material, a magnetization-fixed layer is provided onthe memory layer via an intermediate layer, and the information isrecorded in the memory layer by using a spin torque magnetizationinversion generated with a current flowing in a lamination direction toinvert magnetization of the memory layer, it is possible to record theinformation by applying a current in the lamination direction. At thistime, since the memory layer includes a multilayer structure layer inwhich a non-magnetic material and an oxide are laminated, it is possibleto decrease the current value that is necessary for inverting thedirection of the magnetization of the memory layer.

On the other hand, it is possible to hold the thermal stability of thememory layer sufficiently owing to a strong magnetic anisotropy energyof a perpendicular magnetization film.

From a viewpoint of decreasing an inversion current and ensuring thethermal stability, attention is drawn to the structure using aperpendicular magnetization film as a memory layer. For example,according to Non-Patent Document 3, the possibility of decreasing aninversion current and ensuring the thermal stability by using aperpendicular magnetization film such as a Co/Ni multilayer film as thememory layer is indicated.

Examples of a magnetic material having a perpendicular magneticanisotropy include a rare earth-transition metal alloy (TbCoFe or thelike), a metal multilayer film (Co/Pd multilayer film or the like), anordered alloy (FePt or the like), and using an interfacial anisotropybetween an oxide and magnetic metal (Co/MgO or the like).

However, a material using an interfacial magnetic anisotropy, that is,material in which a magnetic material including Co or Fe is laminated onMgO being a tunnel barrier is promising in view of the adoption of atunnel junction structure to realize a high magnetoresistance changeratio that provides a large read-out signal in the ST-MRAM, withconsideration of heat resistance or easiness in manufacturing.

However, the anisotropy energy of a perpendicular magnetic anisotropyarising from an interfacial magnetic anisotropy is smaller than that ofa crystal magnetic anisotropy, a single ion anisotropy, or the like, andis reduced as the thickness of the magnetic layer increases.

In view of the above, in the present disclosure, a ferromagneticmaterial of the memory layer is a Co—Fe—B layer, and the memory layer isformed to include a laminated structure including an oxide and anon-magnetic layer. Accordingly, the anisotropy in the memory layer isenhanced.

Moreover, according to the configuration of the memory apparatus of thepresent disclosure, a current in the lamination direction is applied tothe memory element through the two types of interconnections and a spintransfer occurs. Thus, it is possible to use a spin torque magnetizationinversion to record information by applying a current in the laminationdirection of the memory element through the two types ofinterconnections.

Moreover, because the thermal stability of the memory layer can besufficiently maintained, it is possible to hold the information storedin the memory element stably, and to realize the miniaturization of thememory apparatus, the improvement of the reliability, and the decreasein the power consumption.

Effect of the Invention

According to the present disclosure, because a memory element having ahigh perpendicular magnetic anisotropy is obtained, it is possible toconfigure a memory element having well-balanced properties whileensuring the thermal stability serving as an information holdingcapacity sufficiently.

Accordingly, it is possible to eliminate the operation error and toobtain an operation margin of the memory element sufficiently.Therefore, it is possible to realize a memory that stably operates witha high reliability.

Moreover, it is possible to decrease the writing current, and todecrease the power consumption when writing is performed on the memoryelement.

Therefore, it is possible to decrease the power consumption of theentire memory apparatus.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A structure diagram of a memory apparatus of an embodiment of thepresent disclosure.

FIG. 2 A cross-sectional view of the memory apparatus of the embodiment.

FIG. 3 Diagrams showing a layered structure of respective memoryelements of the embodiment.

FIG. 4 Diagrams showing a laminated structure of respective samples forexperiments of the memory element of the embodiment.

FIG. 5 A diagram showing an experimental result of the temperaturechange of the magnetic anisotropy in different laminated structures(samples 1 to 5) of the memory element of the embodiment.

FIG. 6 A diagram showing an experimental result of the temperaturechange of the magnetic anisotropy in different laminated structures(samples 3, 6, and 7) of the memory element of the embodiment.

FIG. 7 Explanatory diagrams of examples of applying a magnetic head ofthe embodiment.

MODE(S) FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present disclosure will be describedin the following order.

<1. Configuration of Memory Apparatus of Embodiment>

<2. Overview of Memory Element of Embodiment>

<3. Specific Configuration of Embodiment>

<4. Experiment>

<5. Modified Example>

<1. Configuration of Memory Apparatus of Embodiment>

First, the configuration of a memory apparatus serving as an embodimentof the present disclosure will be described.

Schematic diagrams of the memory apparatus of the embodiment are shownin FIG. 1 and FIG. 2 . FIG. 1 is a perspective view and FIG. 2 is across-sectional view.

As shown in FIG. 1 , the memory apparatus of the embodiment includes,for example, a memory element 3 disposed in the vicinity of theintersection point of two types of address interconnections (e.g., aword line and a bit line) perpendicular to each other, which serves asthe ST-MRAM and is capable of holding information based on amagnetization state.

That is, a drain area 8, a source area 7, and a gate electrode 1constituting a transistor for selection that selects each memoryapparatus are formed on a portion separated by an element isolationlayer 2 of a semiconductor substrate 10 such as a silicon substrate. Ofthese, the gate electrode 1 serves also as one address interconnection(word line) extending in the back and forth direction in the figure.

The drain region 8 is formed commonly with right and left transistorsfor selection in FIG. 1 , and an interconnection 9 is connected to thedrain region 8.

Then, the memory element 3 having a memory layer that inverts amagnetization direction thereof by a spin torque magnetization inversionis disposed between the source region 7 and a bit line 6 that isdisposed at an upper side and extends in the right-left direction inFIG. 1 . The memory element 3 is configured with, for example, amagnetic tunnel junction element (MTJ element).

As shown in FIG. 2 , the memory element 3 has two magnetic layers 15 and17. In the two magnetic layers 15 and 17, one magnetic layer is set as amagnetization-fixed layer 15 in which the direction of magnetization M15is fixed, and the other magnetic layer is set as a magnetization-freelayer in which the direction of magnetization M17 varies, that is,memory layer 17.

Moreover, the memory element 3 is connected to the bit line 6 and thesource region 7 through upper and lower contact layers 4, respectively.

Accordingly, when a current in the vertical direction is applied to thememory element 3 through the two types of address interconnections 1 and6, the direction of the magnetization M17 of the memory layer 17 can beinverted by a spin torque magnetization inversion.

In such a memory apparatus, it is necessary to perform writing with acurrent equal to or less than the saturation current of the selectiontransistor, and it is known that the saturation current of thetransistor decreases along with miniaturization. Therefore, in order tominiaturize the memory apparatus, it is favorable that spin transferefficiency be improved and the current flowing to the memory element 3be decreased.

Moreover, it is necessary to secure a high magnetoresistance changeratio to amplify a read-out signal. In order to realize this, it iseffective to adopt the above-described MTJ structure, that is, toconfigure the memory element 3 in such a manner that an intermediatelayer is used as a tunnel insulating layer (tunnel barrier layer)between the two magnetic layers 15 and 17.

In the case where the tunnel insulating layer is used as theintermediate layer, the amount of the current flowing to the memoryelement 3 is restricted to prevent the insulation breakdown of thetunnel insulating layer from occurring. That is, it is favorable torestrict the current necessary for the spin torque magnetizationinversion from the viewpoint of securing reliability with respect torepetitive writing of the memory element 3. It should be noted that thecurrent necessary for the spin torque magnetization inversion is alsocalled as inversion current, memory current, or the like in some cases.

Moreover, because the memory apparatus is a non-volatile memoryapparatus, it is necessary to stably store the information written by acurrent. That is, it is necessary to secure stability (thermalstability) with respect to thermal fluctuations in the magnetization ofthe memory layer.

In the case where the thermal stability of the memory layer is notsecured, an inverted magnetization direction may be re-inverted due toheat (temperature in an operational environment), which results in awriting error.

The memory element 3 (ST-MRAM) in the memory apparatus is advantageousin scaling compared to the MRAM in the related art, that is,advantageous in that the volume of the memory layer can be small.However, as the volume is small, the thermal stability may bedeteriorated as long as other characteristics are the same.

As the capacity increase of the ST-MRAM proceeds, the volume of thememory element 3 becomes smaller, so that it is an important problem tosecure the thermal stability.

Therefore, in the memory element 3 of the ST-MRAM, the thermal stabilityis a significantly important property, and it is necessary to design thememory element in such a manner that the thermal stability thereof issecured even if the volume is decreased.

<2. Overview of Memory Element of Embodiment>

Next, the overview of the memory element serving as the embodiment ofthe present disclosure will be described.

The embodiment of the present disclosure records information byinverting the magnetization direction of the memory layer of the memoryelement by the above-mentioned spin torque magnetization inversion.

The memory layer is composed of a magnetic material including aferromagnetic layer, and holds the information based on themagnetization state (magnetic direction) of the magnetic material.

FIG. 3 show an example of the respective layered structures of thememory elements 3 and 20.

The memory element 3 has a layered structure, for example, as shown inFIG. 3A, and includes the memory layer 17 and the magnetization-fixedlayer 15 as the at least two ferromagnetic layers, and an intermediatelayer 16 disposed between the two magnetic layers.

The memory layer 17 has magnetization perpendicular to a film face inwhich the direction of the magnetization is changed corresponding to theinformation.

The magnetization-fixed layer 15 has magnetization perpendicular to afilm face that becomes a base of the information stored in the memorylayer 17.

The intermediate layer 16 is formed of a non-magnetic material and isprovided between the memory layer 17 and the magnetization-fixed layer15.

Then, by injecting spin polarized electrons in a lamination direction ofthe layered structure having the memory layer 17, the intermediate layer16, and the magnetization-fixed layer 15, the magnetization direction ofthe memory layer 17 is changed, whereby the information is recorded inthe memory layer 17.

Here, the spin torque magnetization inversion will be briefly described.

Electrons have two types of spin angular momentums. The states of thespin are defined temporarily as up and down. The numbers of up spin anddown spin electrons are the same in the non-magnetic material, but thenumbers of up spin and down spin electrons differ in the ferromagneticmaterial. In two ferromagnetic layers, i.e., the magnetization-fixedlayer 15 and the memory layer 17, constituting the ST-MRAM, the casewhere the directions of the magnetic moment of each layer are in areverse direction and the electrons are moved from themagnetization-fixed layer 15 to the memory layer 17 will be considered.

The magnetization-fixed layer 15 is a fixed magnetic layer having thedirection of the magnetic moment fixed by high coercive force.

The electrons passed through the magnetization-fixed layer 15 are spinpolarized, that is, the numbers of up spin and down spin electronsdiffers. When the thickness of the intermediate layer 16 that is thenon-magnetic layer is made to be sufficiently thin, the electrons reachthe other magnetic material, that is, the memory layer 17 before thespin polarization is mitigated by passing through themagnetization-fixed layer 15 and the electrons become a commonnon-polarized state (the numbers of up spin and down spin electrons arethe same) in a non-polarized material.

A sign of the spin polarization in the memory layer 17 is reversed, sothat a part of the electrons is inverted for lowering the system energy,that is, the direction of the spin angular momentum is changed. At thistime, because the entire angular momentum of the system is necessary tobe conserved, a reaction equal to the total angular momentum change bythe electron, the direction of which is changed, is applied also to themagnetic moment of the memory layer 17.

In the case where the current, that is, the number of electrons passedthrough per unit time is small, the total number of electrons, thedirections of which are changed, becomes small, so that the change inthe angular momentum occurring in the magnetic moment of the memorylayer 17 becomes small, but when the current is increased, it ispossible to apply large change in the angular momentum within a unittime.

The time change of the angular momentum is a torque, and when the torqueexceeds a threshold value, the magnetic moment of the memory layer 17starts a precession, and rotates 180 degrees due to its uniaxialanisotropy to be stable. That is, the inversion from the reversedirection to the same direction occurs.

When the magnetization directions are in the same direction and theelectrons are made to reversely flow from the memory layer 17 to themagnetization-fixed layer 15, the electrons are then reflected at themagnetization-fixed layer 15. When the electrons that are reflected andspin-inverted enter the memory layer 17, a torque is applied and themagnetic moment can be inverted to the reverse direction. However, atthis time, the amount of current necessary for causing the inversion islarger than that in the case of inverting from the reverse direction tothe same direction.

The inversion of the magnetic moment from the same direction to thereverse direction is difficult to intuitively understand, but it may beconsidered that because the magnetization-fixed layer 15 is fixed, themagnetic moment cannot be inverted and the memory layer 17 is invertedfor conserving the angular momentum of the entire system. Thus, therecording of 0/1 is performed by applying a current having apredetermined threshold value or more, which corresponds to eachpolarity, from the magnetization-fixed layer 15 to the memory layer 17or in a reverse direction thereof.

Reading of information is performed by using a magnetoresistive effectsimilarly to the MRAM in the related art. That is, as is the case withthe above-described recording, a current is applied in a directionperpendicular to the film face. Then, a phenomenon in which anelectrical resistance shown by the element varies depending on whetheror not the magnetic moment of the memory layer 17 is the same or reversedirection to the magnetic moment of the magnetization-fixed layer 15 isused.

A material used for the intermediate layer 16 between themagnetization-fixed layer 15 and the memory layer 17 may be a metallicmaterial or an insulating material, but the insulating material may beused for the intermediate layer to obtain a relatively high read-outsignal (resistance change ratio), and to realize the recording by arelatively low current. The element at this time is called aferromagnetic tunnel junction (Magnetic Tunnel Junction: MTJ) element.

A threshold value Ic of the current necessary to inverse themagnetization direction of the magnetic layer by the spin torquemagnetization inversion is different depending on whether an easy axisof magnetization of the magnetic layer is an in-plane direction or aperpendicular direction.

Although the memory elements 3 and 20 of this embodiment areperpendicular magnetization-type, in an in-plane magnetization-typememory element in the related art, the inversion current for invertingthe magnetization direction of the magnetic layer is represented byIc_para.

When the direction is inverted from the same direction to the reversedirection, the equation holds, Ic_para=(A·α·Ms·V/g(0)/P) (Hk+2πMs). Whenthe direction is inverted from the reverse direction to the samedirection, the equation holds, Ic_para=−(A·α·Ms·V/g(π)/P) (Hk+2πMs).

It should be noted that the same direction and the reverse directiondenote the magnetization directions of the memory layer based on themagnetization direction of the magnetization-fixed layer, and are alsoreferred to as a parallel direction and a non-parallel direction,respectively.

On the other hand, in the perpendicular magnetization-type memoryelement according to this example, the inversion current is representedby Ic_perp. When the direction is inverted from the same direction tothe reverse direction, the equation holds, Ic_perp=(A·αMs·V/g(0)/P)(Hk−4πMs). When the direction is inverted from the reverse direction tothe same direction, the equation holds, Ic_perp=−(A·α·Ms·V/g(π)/P)(Hk−4πMs).

It should be noted that A represents a constant, α represents a dampingconstant, Ms represents a saturation magnetization, V represents anelement volume, P represents a spin polarizability, g(0) and g(π)represent coefficients corresponding to efficiencies of the spin torquetransmitted to the other magnetic layer in the same direction and thereverse direction, respectively, and Hk represents the magneticanisotropy.

In the respective equations, when the term (Hk−4πMs) in theperpendicular magnetization type is compared with the term (Hk+2πMs) inthe in-plane magnetization type, it can be understood that theperpendicular magnetization type is suitable to decrease a recordingcurrent.

Here, a relationship between an inversion current Ic0 and a thermalstability index Δ is represented by the following (Math. 1).

$\begin{matrix}{{I_{c}0} = {\left( \frac{4ek_{B}T}{\hslash} \right)\left( \frac{\alpha\Delta}{\eta} \right)}} & \left\lbrack {{Math}.1} \right\rbrack\end{matrix}$

It should be noted that e represents an electron charge, η representsspin injection efficiency, h with bar represents a decreased Planckconstant, α represents a damping constant, k_(B) represents a Boltzmannconstant, and T represents a temperature.

In this embodiment, the memory element includes the magnetic layer(memory layer 17) capable of holding the information based on themagnetization state, and the magnetization-fixed layer 15 in which themagnetization direction is fixed.

It has to hold the written information to exist as a memory. It isjudged by the value of the thermal stability index Δ(=KV/k_(B)T) as anindex of ability to hold the information. The Δ is represented by the(Math. 2).

$\begin{matrix}{\Delta = {\frac{KV}{k_{B}T} = \frac{M_{S}VH_{K}}{2k_{B}T}}} & \left\lbrack {{Math}.2} \right\rbrack\end{matrix}$

Here, Hk represents an effective anisotropic magnetic field, k_(B)represents a Boltzmann constant, T represents a temperature, Msrepresents a saturated magnetization amount, V represents a volume ofthe memory layer, and K represents the anisotropic energy.

The effective anisotropic magnetic field Hk is affected by a shapemagnetic anisotropy, an induced magnetic anisotropy, a crystal magneticanisotropy and the like. Assuming a single-domain coherent rotationmodel, this will be equal to coercive force.

The thermal stability index Δ and the threshold value Ic of the currentoften have the trade-off relationship. Accordingly, in order to maintainthe memory characteristics, the trade-off often becomes an issue.

In practice, in a circle TMR element having, for example, the memorylayer 17 with a thickness of 2 nm and a plane pattern with a diameter of100 nm, the threshold value of the current to change the magnetizationstate of the memory layer is about one hundred to several hundreds ofμA.

In contrast, in the normal MRAM that inverts the magnetization using acurrent magnetic field, the written current exceeds several mA.

Accordingly, in the case of the ST-MRAM, the threshold value of thewritten current becomes sufficiently low, as described above. Therefore,it can be seen that it is effective to decrease the power consumption ofthe integrated circuit.

In addition, because the interconnections for generating the currentmagnetic field used in the normal MRAM are unnecessary, it isadvantageous over the normal MRAM in terms of the integration.

Then, when the spin torque magnetization inversion is performed, acurrent is applied directly into the memory element to write (record)the information. Therefore, in order to select a memory cell to whichwriting is performed, the memory element is connected to a selectiontransistor to configure the memory cell.

In this case, the current flowing to the memory element is limited bythe amount of the current that can flow to the selection transistor (thesaturation current of the selection transistor).

In order to decrease the recording current, the perpendicularmagnetization-type is desirably used, as described above. Moreover, theperpendicular magnetization film can generally provide higher magneticanisotropy than the in-plane magnetization film, and therefore isdesirable in that the Δ is kept greater.

Examples of the magnetic material having the perpendicular anisotropyinclude a rare earth-transition metal alloy (TbCoFe or the like), ametal multilayer film (Co/Pd multilayer film or the like), an orderedalloy (FePt or the like), and using an interfacial anisotropy between anoxide and magnetic metal (Co/MgO or the like). When the rareearth-transition metal alloy is diffused and crystallized by beingheated, the perpendicular magnetic anisotropy is lost, and therefore therare earth-transition metal alloy is not favorable as the ST-MRAMmaterial.

It is known that also the metal multilayer film is diffused when beingheated, and the perpendicular magnetic anisotropy is degraded. Becausethe perpendicular magnetic anisotropy is developed when it has aface-centered cubic (111) orientation, it is difficult to realize a(001) orientation necessary for a high polarizability layer includingMgO, and Fe, CoFe, and CoFeB disposed adjacent to MgO. An L10 orderedalloy is stable even at high temperature and shows the perpendicularmagnetic anisotropy in the (001) orientation. Therefore, theabove-mentioned problem is not induced. However, the L10 ordered alloyhas to be heated at sufficiently high temperature of 500° C. or moreduring the production, or atoms should be arrayed regularly by beingheated at a high temperature of 500° C. or more after the production. Itmay induce unfavorable diffusion or an increase in interfacial roughnessin other portions of a laminated film such as a tunnel barrier.

In contrast, the material utilizing interfacial magnetic anisotropy,i.e., the material including MgO being the tunnel barrier and a Co-basedor Fe-based material laminated thereon hardly induces any of theabove-mentioned problems, and is therefore highly expected as the memorylayer material of the ST-MRAM.

However, in order to increase the density of the minute element, itneeds to further decrease the power consumption of the entire memoryapparatus, particularly, to decrease the writing current, similarly toother materials.

In order to solve this, the writers of the present disclosure created astructure in which the memory layer 17 is formed to include a multilayerstructure layer in which a non-magnetic material and an oxide arelaminated, as shown in FIG. 3B.

Accordingly, it is possible to obtain the memory element 20 having ahigh perpendicular magnetic anisotropy, to sufficiently secure thethermal stability, which is an information holding capacity, and toconfigure the memory element 20 having well-balanced properties.

Moreover, operation errors can be eliminated, and operation margins ofthe memory element 20 can be sufficiently obtained. Thus, it is possibleto realize a memory that stably operates with a high reliability.

Moreover, it is possible to decrease the writing current and to decreasethe power consumption when performing writing into the memory element20.

As a result, it is possible to decrease the power consumption of theentire memory apparatus.

Furthermore, in view of the saturated current value of the selectiontransistor, as the non-magnetic intermediate layer 16 between the memorylayer 17 and the magnetization-fixed layer 15, the magnetic tunneljunction (MTJ) element is configured using the tunnel insulating layerincluding an insulating material.

This is because by configuring the magnetic tunnel junction (MTJ)element using the tunnel insulating layer, it is possible to make amagnetoresistance change ratio (MR ratio) high compared to a case wherea giant magnetoresistive effect (GMR) element is configured using anon-magnetic conductive layer, and to increase the read-out signalstrength.

Then, in particular, by using magnesium oxide (MgO) as the material ofthe intermediate layer 16 serving as the tunnel insulating layer, it ispossible to make the magnetoresistance change ratio (MR ratio) high.

Moreover, generally, the spin transfer efficiency depends on the MRratio, and as the MR ratio is high, the spin transfer efficiency isimproved, and therefore it is possible to decrease the magnetizationinversion current density.

Therefore, when magnesium oxide is used as the material of the tunnelinsulating layer and the memory layer 17 is used, it is possible todecrease the writing threshold current by the spin torque magnetizationinversion and therefore it is possible to perform the writing(recording) of information with a small current. Moreover, it ispossible to increase the read-out signal strength.

Accordingly, it is possible to decrease the writing threshold current bythe spin torque magnetization inversion by securing the MR ratio (TMRratio), and to perform the writing (recording) of information with asmall current. Moreover, it is possible to increase the read-out signalstrength.

As described above, in the case where the tunnel insulating layer isformed of the magnesium oxide (MgO) film, it is desirable that the MgOfilm be crystallized and a crystal orientation be maintained in the(001) direction.

It should be noted that in this embodiment, in addition to aconfiguration formed of the magnesium oxide, the intermediate layer 16(tunnel insulating layer) disposed between the memory layer 17 and themagnetization-fixed layer 15 may be configured by using, for example,various insulating materials, dielectric materials, and semiconductorssuch as aluminum oxide, aluminum nitride, SiO₂, Bi₂O₃, MgF₂, CaF,SrTiO₂, AlLaO₃, and Al—N—O.

An area resistance value of the tunnel insulating layer has to becontrolled to several tens Ωμm² or less from the viewpoint of obtaininga current density necessary for inverting the magnetization direction ofthe memory layer 17 by the spin torque magnetization inversion.

Then, in the tunnel insulating layer formed of the MgO film, the filmthickness of the MgO film has to be set to 1.5 nm or less so that thearea resistance value is in the range described above.

Moreover, in the embodiment of the present disclosure, a cap layer 18 isdisposed adjacent to the memory layer 17, and the cap layer may form anoxide layer.

As the oxide of the cap layer 18, MgO, aluminum oxide, TiO₂, SiO₂,Bi₂O₃, SrTiO₂, AlLaO₃, or Al—N—O may be used, for example.

Moreover, it is desirable to make the memory element small in size toeasily invert the magnetization direction of the memory layer 17 with asmall current.

Therefore, the area of the memory element is favorably set to 0.01 μm²or less.

It is fovarable that the film thickness of each of themagnetization-fixed layer 15 and the memory layer 17 be 0.5 nm to 30 nm.

Other configurations of the memory element may be the same as theconfiguration of a memory element that records information by the spintorque magnetization inversion in the related art.

The magnetization-fixed layer 15 may be configured in such a manner thatthe magnetization direction is fixed by only a ferromagnetic layer or byusing an antiferromagnetic coupling of an antiferromagnetic layer and aferromagnetic layer.

Moreover, the magnetization-fixed layer 15 may have a configuration of asingle ferromagnetic layer, or a laminated ferri-pinned structure inwhich a plurality of ferromagnetic layers are laminated via anon-magnetic layer.

As a material of the ferromagnetic layer making up themagnetization-fixed layer 15 having the laminated ferri-pinnedstructure, Co, CoFe, CoFeB, or the like may be used. Moreover, as amaterial of the non-magnetic layer, Ru, Re, Ir, Os, or the like may beused.

As a material of the antiferromagnetic layer, a magnetic material suchas an FeMn alloy, a PtMn alloy, a PtCrMn alloy, an NiMn alloy, an IrMnalloy, NiO, and Fe₂O₃ may be exemplified.

Moreover, magnetic properties may be adjusted by adding a non-magneticelement such as Ag, Cu, Au, Al, Si, Bi, Ta, B, C, O, N, Pd, Pt, Zr, Hf,Ir, W, Mo, and Nb to these magnetic materials, or in addition to this, acrystalline structure or various physical properties such as acrystalline property and a stability of a substance may be adjusted.

Moreover, in relation to a film configuration of the memory element,there is no problem if the memory layer 17 may be disposed at the lowerside of the magnetization-fixed layer 15. In this case, the role of theabove-described conductive oxide cap layer is made by a conductive oxideunderlying layer.

<3. Specific Configuration of Embodiment>

Next, a specific configuration of the embodiment will be described.

The memory apparatus includes the memory element 3, which is capable ofholding information based on a magnetization state, disposed in thevicinity of the intersection point of the two kinds of addressinterconnections 1 and 6 (e.g., a word line and a bit line) that areperpendicular to each other, as shown in FIGS. 1 and 2 .

Then, when a current in the vertical direction is applied to the memoryelement 3 through the two types of address interconnections 1 and 6, themagnetization direction of the memory layer 17 can be inverted by thespin torque magnetization inversion.

FIGS. 3A and 3B each show an example of the layered structure of thememory element (ST-MRAM) of the embodiment.

As described above, in the memory element 3 shown in FIG. 3A, anunderlying layer 14, the magnetization-fixed layer 15, the intermediatelayer 16, the memory layer 17, and the cap layer 18 are laminated in thestated order from the lower layer side.

In this case, the magnetization-fixed layer 15 is disposed under thememory layer 17 in which the direction of the magnetization M17 isinverted by the spin injection.

In the spin injection-type memory, “0” and “1” of information aredefined by a relative angle between the magnetization M17 of the memorylayer 17 and the magnetization M15 of the magnetization-fixed layer 15.

The intermediate layer 16 that serves as a tunnel barrier layer (tunnelinsulating layer) is provided between the memory layer 17 and themagnetization-fixed layer 15, and an MTJ element is configured by thememory layer 17 and the magnetization-fixed layer 15. Moreover, theunderlying layer 14 is provided under the magnetization-fixed layer 15.

The memory layer 17 is composed of a ferromagnetic material having amagnetic moment in which the direction of the magnetization M17 isfreely changed in a direction perpendicular to a layer face. Themagnetization-fixed layer 15 is composed of a ferromagnetic materialhaving a magnetic moment in which the magnetization M15 is fixed in adirection perpendicular to a film face.

Information is recorded by the magnetization direction of the memorylayer 15 having uniaxial anisotropy. Writing is performed by applying acurrent in the direction perpendicular to the film face, and inducingthe spin torque magnetization inversion. Thus, the magnetization-fixedlayer 15 is disposed under the memory layer 15 in which themagnetization direction is inverted by the spin injection, and is toserve as the base of the stored information (magnetization direction) ofthe memory layer 17.

Because the magnetization-fixed layer 15 is the base of the information,the magnetization direction should not be changed by recording orreading-out. However, the magnetization-fixed layer 15 does notnecessarily need to be fixed to the specific direction, and only needsto be difficult to move by increasing the coercive force, the filmthickness, or the magnetic damping constant as compared with the memorylayer 17.

The intermediate layer 16 is formed of a magnesium oxide (MgO) layer,for example. In this case, it is possible to make a magnetoresistancechange ratio (MR ratio) high.

When the MR ratio is thus made to be high, the spin injection efficiencyis improved, and therefore it is possible to decrease the currentdensity necessary for inverting the direction of the magnetization M17of the memory layer 17.

It should be noted that the intermediate layer 16 may be configured byusing, for example, various insulating materials, dielectric materials,and semiconductors such as aluminum oxide, aluminum nitride, SiO₂,Bi₂O₃, MgF₂, CaF, SrTiO₂, AlLaO₃, and Al—N—O, as well as magnesiumoxide.

As the underlying layer 14 and the cap layer 18, a variety of metalssuch as Ta, Ti, W, and Ru and a conductive nitride such as TiN can beused. Moreover, the underlying layer 14 and the cap layer 18 may includea single layer or a plurality of layers in which different materials arelaminated.

The structure of the memory element 20 shown in FIG. 3B is differentfrom that of the memory element 3 in the structure of the memory layer17. The memory layer 17 of the memory element 20 includes a multilayerstructure layer in which an oxide layer 22 and a non-magnetic layer 21are laminated.

Such a multilayer structure layer of the oxide layer 22 and thenon-magnetic material layer 21 is not limited to one layer as shown inFIG. 3B, and may be formed of two or more layers.

As the oxide 22, at least one of silicon oxide, magnesium oxide,tantalum oxide, aluminum oxide, cobalt oxide, zirconium oxide, titaniumoxide, and chromium oxide can be selected.

As the non-magnetic material, at least one of Cu, Ag, Au, V, Ta, Zr, Nb,Hf, W, Mo, and Cr can be selected.

The memory layer 17 includes a multilayer structure layer formed of thenon-magnetic layer 21 and the oxide layer 22, which represents that aheating mechanism in which the temperature rise of the memory layer 17is increased as compared to a given environment temperature is provided.

Therefore, in the case where the above-mentioned heating mechanismhaving a high thermal conductivity provides the same temperature rise,the inversion of the magnetization of the memory layer 17 of the memoryelement 20 according to the embodiment is enhanced and it is possible todecrease the recording current. Furthermore, in a viewpoint of thethermal stability, a magnetic anisotropy is increased and holdingproperties (capacity to hold information) are improved.

According to the above-described embodiment shown in FIGS. 3A and 3B,particularly, the composition of the memory layer 17 of the memoryelement is adjusted in such a manner that the magnitude of the effectivediamagnetic field that the memory layer 17 receives is smaller than thesaturated magnetization amount Ms of the memory layer 17.

In other words, the effective diamagnetic field that the memory layer 17receives is decreased to be smaller than the saturated magnetizationamount Ms of the memory layer 17 by selecting the ferromagnetic materialCo—Fe—B composition of the memory layer 17.

The memory elements 3 and 20 of the embodiment can be manufactured bycontinuously forming from the underlying layer 14 to the cap layer 18 ina vacuum apparatus, and then by forming a pattern of the memory elements3 and 20 by processing such as etching.

According to this embodiment, because the memory layer 17 of the memoryelements 3 and 20 is a perpendicular magnetization film, it is possibleto decrease the amount of writing current necessary for inverting thedirection of the magnetization M17 of the memory layer 17.

As described above, because the thermal stability, which is aninformation holding capacity, can be sufficiently secured, it ispossible to configure the memory elements 3 and 20 having well-balancedproperties.

Accordingly, operation errors can be eliminated, and the operationmargins can be sufficiently obtained. Thus, it is possible to cause itto stably operate.

Accordingly, it is possible to realize a memory apparatus that stablyoperates with a high reliability.

Moreover, it is possible to decrease the writing current and to decreasethe power consumption when performing writing.

In particular, in the memory layer 20 including a multilayer structurelayer in which the oxide layer 22 and the non-magnetic layer 21 arelaminated, because the multilayer structure layer serves as a heatingmechanism, the inversion of the magnetization is enhanced and therecording current is decreased. Furthermore, in a viewpoint of thethermal stability, a magnetic anisotropy is increased and holdingproperties (capacity to hold information) are improved

Therefore, it is possible to decrease the power consumption of theentire memory apparatus including the memory elements 3 and 20 of thisembodiment.

Moreover, the memory apparatus that includes the memory elements 3 and20 shown in FIG. 3 and has a configuration shown in FIG. 1 has anadvantage in that a general semiconductor MOS forming process may beapplied when the memory apparatus is manufactured. Therefore, it ispossible to apply the memory apparatus of this embodiment as a generalpurpose memory.

<4. Experiment Regarding Embodiment>

Here, in regard to the configuration of the memory elements 3 and 20 ofthis embodiment shown in FIG. 3A and FIG. 3B, experiments in whichsamples were prepared and then characteristics thereof were examinedwere conducted.

The conducted experiments are an experiment 1 and an experiment 2. Theexperiment 1 was conducted to obtain the temperature change ofperpendicular anisotropy. The experiment 2 was conducted to calculatethe value of thermal stability index by the measurement of a magneticresistance curve and to measure the value of an inversion current.

In an actual memory apparatus, as shown in FIG. 1 , a semiconductorcircuit for switching or the like is present in addition to the memoryelements 3 and 20, but here, the examination was conducted on a wafer inwhich only a memory element is formed in order to check themagnetization inversion properties of the memory layer 17 adjacent tothe cap layer 18.

As the sample of a memory element for experiments, as shown in FIG. 4 ,with the common layers of:

-   -   Underlying layer 14: Laminated film of a Ta film having a film        thickness of 10 nm and an Ru film having a film thickness of 10        nm;    -   Magnetization-fixed layer 15: Laminated film of CoPt:2 nm/Ru:0.7        nm/[Co20Fe80]70B30:1.2 nm;    -   Intermediate layer (tunnel insulating layer) 16: MgO film having        a film thickness of 1.0 nm; and    -   Cap layer 18: /Ta:5 nm film/,        the memory layer 17 has the following layered structure, and 7        types of samples are prepared.

As shown in FIG. 4A to G,

-   -   Sample 1 (FIG. 4A) Memory layer 17: [Co20Fe80]70B30 having a        film thickness of 2.2 nm    -   Sample 2 (FIG. 4B) Memory layer 17: [Co20Fe80]70B30 having a        film thickness of 1.1 nm/Ta having a film thickness of 0.2        nm/[Co20Fe80]70B30 having a film thickness of 1.1 nm    -   Sample 3 (FIG. 4C) Memory layer 17: [Co20Fe80]80B20 having a        film thickness of 1.1 nm/Layered structure of magnesium oxide        having a film thickness of 0.1 nm and Ta having a film thickness        of 0.1 nm/[Co20Fe80]80B20 having a film thickness of 1.1 nm    -   Sample 4 (FIG. 4D) Memory layer 17: [Co20Fe80]80B20 having a        film thickness of 1.1 nm/aluminum oxide having a film thickness        of 0.1 nm and Ta having a film thickness of 0.1        nm/[Co20Fe80]80B20 having a film thickness of 1.1 nm    -   Sample 5 (FIG. 4E) Memory layer 17: [Co20Fe80]80B20 having a        film thickness of 1.1 nm/MgO having a film thickness of 0.1 nm        and Cr film having a film thickness of 0.1 nm/[Co20Fe80]80B20        having a film thickness of 1.1 nm    -   Sample 6 (FIG. 4F) Memory layer 17: [Co20Fe80]80B20 having a        film thickness of 0.8 nm/MgO having a film thickness of 0.1 nm        and Ta having a film thickness of 0.1 nm/[Co20Fe80]80B20 having        a film thickness of 0.7 nm/MgO having a film thickness of 0.1 nm        and Ta having a film thickness of 0.1 nm/[Co20Fe80]80B20 having        a film thickness of 0.7 nm    -   Sample 7 (FIG. 4G) Memory layer 17: [Co20Fe80]80B20 having a        film thickness of 0.8 nm/MgO having a film thickness of 0.1 nm        and Ta having a film thickness of 0.1 nm/Co20Fe80B30 having a        film thickness of 0.7 nm/Ta having a film thickness of 0.1 nm        and MgO having a film thickness of 0.1 nm/[Co20Fe80]80B20 having        a film thickness of 0.7 nm (structure sandwiched from up and        down by MgO layers)

A thermally-oxidized film having a thickness of 300 nm was formed on asilicon substrate having a thickness of 0.725 mm, and each sample of thememory element having the above-described configuration was formedthereon. Moreover, a Cu film (to be a word line) having a film thicknessof 100 nm, which was not shown, was provided between the underlyinglayer and the silicon substrate.

Each layer other than the insulating layer was formed using a DCmagnetron sputtering method. The insulating layer using an oxide wasoxidized in an oxidation chamber after a metal layer was formed using anRF magnetron sputtering method or a DC magnetron sputtering method.After each layer of the memory element was formed, heat treatment wasperformed at 300° C. for 1 hour in a magnetic field heat treatmentfurnace.

EXPERIMENT 1

This experiment was conducted to obtain the temperature change ofperpendicular anisotropy of each sample described above.

The magnetization curve of the memory element is measured by magnetickerr effect measurement and a Vibrating Sample Magnetometer to obtainthe temperature change of the perpendicular anisotropy. For themeasurement, not the element after being subject to minute processingbut a bulk film portion having a size of about 8 mm×8 mm, which wasspecially provided on a wafer for magnetization curve evaluation, wasused. Moreover, the measurement magnetic field was applied in thedirection perpendicular to a film face.

FIG. 5 shows the obtained change of the perpendicular magneticanisotropy of the samples 1 to 5 with respect to environmenttemperature. The temperature change of the magnetic anisotropy of thesample 2 and the samples 3 to 5 is larger than that of the sample 1.However, even in this case, there is no problem because theperpendicular magnetic anisotropy of the sample 2 and the samples 3 to 5is sufficiently larger than that of the sample 1.

Moreover, when the sample 2 is compared with the samples 3 to 5, thebehavior of the magnetic anisotropy of being larger than that of thesample 2 at the environment temperature of about 60° C. in the exampleand conversely, being lower than that of the sample 2 at the environmenttemperature of about 100° C. is observed.

This provides a thought that the multilayer structure layer of thenon-magnetic layer and the oxide layer in the memory layer 17 functionsas a heating mechanism that increases the temperature rise of the memorylayer 17 as compared to a given environment temperature (hereinafter,heater layer).

The reason of the larger temperature rise can be considered as follows.Normally, the non-magnetic layer that functions as the heater layer inthe memory layer 17 is distributed in a uniform layer form. Here, it isestimated that if the oxide layer of an ultrashallow film issimultaneously formed in the memory layer 17, the heater layer isdistributed by the oxide layer having relatively large concavity andconvexity and the surface area thereof that is in contact with themagnetic material in the memory layer 17 is increased, thereby improvingthe effect as the heater layer.

The principle of the STT-MRAM is based on magnetization inversion byspin torque injection. However, it is estimated that in an actualelement, the temperature of the memory layer 17 is increased by 100° C.or more by the current flowing during the inversion. In the case wherethe samples 3 to 5 in which the heater layer having a high thermalconductivity is introduced are given the same temperature rise as thatof a normal element, the magnetization inversion is enhanced because themagnetic anisotropy is significantly changed. Therefore, it isconsidered possible to decrease the recording current.

Moreover, in a viewpoint of the thermal stability, the samples 3 to 5 inwhich the heater layer having a high thermal conductivity is introducedhave significantly different magnetic anisotropies at about 60° C.Because the interfacial anisotropy of the oxide layer contributes to theperpendicular magnetization in a Co—Fe—B alloy or the like, this furtherincreases the perpendicular magnetic anisotropy in the holdingtemperature range. From this, it can be said that those in which theheater layer having a high thermal conductivity is introduced haveadvantages in also the holding properties.

Furthermore, a plurality of multilayer structure layers may be formed inthe memory layer as a method of enhancing the effect of the heaterlayer. FIG. 6 shows the temperature change of the perpendicular magneticanisotropies of the samples 3 and the samples 6 and 7. In the samples 6and 7 having a plurality of multilayer structure layers of thenon-magnetic layer and the oxide layer, the decrease in theperpendicular magnetic anisotropy with respect to the heatingtemperature is larger and the recording current is expected to be lowerthan those having one multilayer structure layer.

In addition, in the sample 7, the decrease in the perpendicular magneticanisotropy is larger than that in the sample 6. This is because thenon-magnetic layers (Ta) to be the heater layer are disposedsymmetrically with respect to the center of the memory layer and themagnetic material in the memory layer sandwiched between the heaterlayers is efficiently affected by the plurality of heater layers, in theexample 7. It is considered that as a result, the change of theperpendicular magnetic anisotropy of the entire memory layer isincreased.

As a result of various studies, if the multilayer structure layer of thenon-magnetic layer and the oxide layer is formed, the effect of theheater layer can be efficiently exerted.

The material of the non-magnetic layer can be selected from at least oneof Cu, Ag, Au, V, Ta, Zr, Nb, Hf, W, Mo, and Cr, and, on the other hand,the oxide layer can be selected from at least one of silicon oxide,magnesium oxide, tantalum oxide, aluminum oxide, cobalt oxide, zirconiumoxide, titanium oxide, and chromium oxide. Moreover, in the experiment,the composition of CO—Fe—B may be changed from about 20 to 40% from aviewpoint of the TMR value or the heat resistance.

EXPERIMENT 2

In this experiment, in order to evaluate the writing properties of thememory element, the calculation of the value of the thermal stabilityindex by the measurement of the magnetoresistance curve and themeasurement of the inversion current value are performed in each sampledescribed above.

A current with a pulse width of 10 μs to 100 ms was applied to thememory element, and the subsequent resistance value of the memoryelement was measured. Furthermore, the amount of currents applied to thememory element was changed, and the current value at which the directionof the magnetization of the memory layer of the memory element isinverted was obtained.

Moreover, the distribution of the coercive force obtained by measuringthe magnetoresistance curve of the memory element a plurality of timescorresponds to the index (Δ) of the holding properties (thermalstability) of the memory element. As the measured distribution of thecoercive force is less, a higher A value is obtained. Then, in order totake into account the variability between memory elements, about 20memory elements having the same configuration were prepared, and theabove-mentioned measurement was performed. Thus, the inversion currentvalue and the average value of the index Δ of the thermal stability wereobtained.

TABLE 1 Index of thermal stability (Δ) Inversion current (MA/cm²) Sample1 28 4.2 Sample 2 45 4.1 Sample 6 48 3.7 Sample 7 45 3.5

In Table 1, evaluation of the magnetization inversion properties inwriting by a current in the samples 1, 2, 6, and 7 was collected. Adifference in the thermal stabilities is caused between the samples 1and 2 by reflecting the adjustment of the magnetic properties due to theexistence or non-existence of the non-magnetic layer.

In the samples 6 and 7, the inversion current density is decreased byabout 10% while maintaining the thermal stability, which exemplifies theresults of the experiment 1. In the sample 7 particularly, it isconsidered that because the magnetic material in the memory layersandwiched between the heater layers by the lamination adding layer isintensively heated, the temperature dependency of the anisotropy of theportion is further increased and the magnetization is invertedpreferentially.

Furthermore, the inverted layer transmits the inversion over the entirememory layer via the magnetic coupling, thereby further decreasing theinversion current density.

The additional laminated structure of the non-magnetic layer and theoxide layer is not limited to the laminated structure in the samples 6and 7 and may be changed in the effective range shown in the experiment1.

Moreover, the underlying layer 14 or the cap layer 18 may include asingle material or may have a laminated structure of a plurality ofmaterials.

Moreover, the magnetization-fixed layer 15 may be a single layer or mayhave a laminated ferri-pinned structure including two ferromagneticlayers and a non-magnetic layer. Moreover, it may have a structureobtained by adding an anti-ferromagnetic film to a laminatedferri-pinned structure film.

<5. Modified Example>

The memory element 3 or the memory element 20 of the present disclosurehas a configuration of the magnetoresistive effect element such as a TMRelement. The magnetoresistive effect element as the TMR element can beapplied to a variety of electronic apparatuses, electric appliances, andthe like including a magnetic head, a hard disk drive equipped with themagnetic head, an integrated circuit chip, a personal computer, aportable terminal, a mobile phone, and a magnetic sensor device, as wellas the above-described memory apparatus.

As an example, FIGS. 7A and 7B each show an application of amagnetoresistive effect element 101 having the structure of theabove-described memory elements 3 and 20 to a composite magnetic head100. It should be noted that FIG. 7A is a perspective view shown bycutting some parts of the composite magnetic head 100 for discerning theinternal configuration, and FIG. 7B is a cross-sectional view of thecomposite magnetic head 100.

The composite magnetic head 100 is a magnetic head used for a hard diskapparatus or the like, and is obtained by forming the magnetoresistiveeffect magnetic head to which the technique of the present disclosure isapplied on a substrate 122. On the magnetoresistive effect magnetichead, an inductive magnetic head is laminated and thus the compositemagnetic head 100 is formed. Here, the magnetoresistive effect magnetichead operates as a reproducing head, and the inductive magnetic headoperates as a recording head. That is, the composite magnetic head 100is configured by combining the reproducing head and the recording head.

The magnetoresistive effect magnetic head mounted on the compositemagnetic head 100 is a so-called shielded MR head, and includes a firstmagnetic shield 125 formed on the substrate 122 via an insulating layer123, the magnetoresistive effect element 101 formed on the firstmagnetic shield 125 via the insulating layer 123, and a second magneticshield 127 formed on the magnetoresistive effect element 101 via theinsulating layer 123. The insulating layer 123 includes an insulatingmaterial such as Al₂O₃ and SiO₂.

The first magnetic shield 125 is for magnetically shielding a lower sideof the magnetoresistive effect element 101, and includes a soft magneticmaterial such as Ni—Fe. On the first magnetic shield 125, themagnetoresistive effect element 101 is formed via the insulating layer123.

The magnetoresistive effect element 101 functions as a magnetosensitiveelement for detecting a magnetic signal from the magnetic recordingmedium in the magnetoresistive effect magnetic head. Then, themagnetoresistive effect element 101 may have the similar filmconfiguration to the above-described memory element 3 or the memoryelement 20.

The magnetoresistive effect element 101 is formed in an almostrectangular shape, and has one side that is exposed to an oppositesurface of the magnetic recording medium. Then, at both ends of themagnetoresistive effect element 101, bias layers 128 and 129 aredisposed. Moreover, connection terminals 130 and 131 that are connectedto the bias layers 128 and 129 are formed. A sense current is suppliedto the magnetoresistive effect element 101 via the connection terminals130 and 131.

Furthermore, above the bias layers 128 and 129, the second magneticshield 127 is disposed via the insulating layer 123.

The inductive magnetic head laminated and formed on the above-describedmagnetoresistive effect magnetic head includes a magnetic core includingthe second magnetic shield 127 and an upper core 132, and a thin filmcoil 133 formed so as to be wound around the magnetic core.

The upper core 132 forms a closed magnetic path together with the secondmagnetic shield 122, is to be the magnetic core of the inductivemagnetic head, and includes a soft magnetic material such as Ni—Fe.Here, the second magnetic shield 127 and the upper core 132 are formedsuch that front end portions thereof are exposed to an opposite surfaceof the magnetic recording medium, and the second magnetic shield 127 andthe upper core 132 come into contact with each other at back endportions thereof. Here, the front end portions of the second magneticshield 127 and the upper core 132 are formed at the opposite surface ofthe magnetic recording medium such that the second magnetic shield 127and the upper core 132 are spaced apart by a predetermined gap g.

That is, in the composite magnetic head 100, the second magnetic shield127 not only magnetically shields the upper layer side of themagnetoresistive effect element 126, but functions as the magnetic coreof the inductive magnetic head. The second magnetic shield 127 and theupper core 132 configure the magnetic core of the inductive magnetichead. Then, the gap g is to be a recording magnetic gap of the inductivemagnetic head.

In addition, above the second magnetic shield 127, thin film coils 133buried in the insulation layer 123 are formed. Here, the thin film coils133 are formed to wind around the magnetic core including the secondmagnetic shield 127 and the upper core 132. Although not shown, bothends of the thin film coils 133 are exposed to the outside, andterminals formed on the both ends of the thin film coil 133 are to beexternal connection terminals of the inductive magnetic head. That is,when a magnetic signal is recorded on the magnetic recording medium, arecording current will be supplied from the external connectionterminals to the thin film coil 132.

The composite magnetic head 121 as described above is equipped with themagnetoresistive effect magnetic head as the reproducing head. Themagnetoresistive effect magnetic head is equipped, as themagnetosensitive element that detects a magnetic signal from themagnetic recording medium, with the magnetoresistive effect element 101to which the technology of the present disclosure is applied. Then, asthe magnetoresistive effect element 101 to which the technology of thepresent disclosure is applied shows the excellent properties asdescribed above, the magnetoresistive effect magnetic head can achievefurther high recording density of magnetic recording.

It should be noted that the present disclosure may also have thefollowing configurations.

-   (1) A memory element, including    -   a layered structure including        -   a memory layer having magnetization perpendicular to a film            face in which a direction of the magnetization is changed            depending on information, the memory layer including a            multilayer structure layer in which a non-magnetic material            and an oxide are laminated, the direction of the            magnetization of the memory layer being changed by applying            a current in a lamination direction of the layered structure            to record the information in the memory layer,        -   a magnetization-fixed layer having magnetization            perpendicular to the film face, which becomes a base of the            information stored in the memory layer, and        -   an intermediate layer that is formed of a non-magnetic            material and is provided between the memory layer and the            magnetization-fixed layer.-   (2) The memory element according to (1) above, in which    -   the non-magnetic material includes at least one of Cu, Ag, Au,        V, Ta, Zr, Nb, Hf, W, Mo, and Cr.-   (3) The memory element according to (1) or (2) above, in which    -   the oxide includes at least one of silicon oxide, magnesium        oxide, tantalum oxide, aluminum oxide, cobalt oxide, zirconium        oxide, titanium oxide, and chromium oxide.-   (4) The memory element according to any one of (1) to (3) above, in    which    -   at least two multilayer structure layers including the        non-magnetic material and the oxide are formed in the memory        layer.-   (5) The memory element according to any one of (1) to (4) above, in    which    -   a ferromagnetic material forming the memory layer is Co—Fe—B.

DESCRIPTION OF REFERENCE NUMERALS

-   1 gate electrode-   2 element isolation layer-   3 memory element-   4 contact layer-   6 bit line-   7 source area-   8 drain area-   9 interconnection-   10 semiconductor substrate-   14 underlying layer-   15 magnetization-fixed layer-   16 intermediate layer-   17 memory layer-   18 cap layer-   21 oxide layer-   22 non-magnetic layer-   100 composite magnetic head-   122 substrate-   123 insulating layer-   125 first magnetic shield-   127 second magnetic shield-   128 129 bias layer-   130 131 connection terminal-   132 upper core-   133 thin film coil

What is claimed is:
 1. A memory device, comprising: a memory layer witha plurality of ferromagnetic material layers, a non-magnetic layer, anda non-magnetic oxide layer; a magnetization-fixed layer; and anintermediate layer between the memory layer and the magnetization-fixedlayer, wherein, the plurality of ferromagnetic material layers include afirst ferromagnetic material layer and a second ferromagnetic materiallayer, the non-magnetic layer is in direct contact with the firstferromagnetic material layer and the non-magnetic oxide layer is indirect contact with the second ferromagnetic material layer, thenon-magnetic layer and the non-magnetic oxide layer are in directcontact with each other and are between the first ferromagnetic materiallayer and the second ferromagnetic material layer, the memory layerincludes a magnetization perpendicular to a film face of the memorylayer and parallel to a thickness direction of the memory device, adirection of the magnetization being changeable, and wherein aperpendicular direction of the magnetization of the memory layer ischangeable by applying a current in the thickness direction of thememory device to record information in the memory layer, the first andsecond ferromagnetic material layers comprising a same ferromagneticmaterial and having a same direction of magnetization.
 2. The memorydevice according to claim 1, wherein the non-magnetic layer is made of ametallic material layer and is not an oxide layer.
 3. The memory deviceaccording to claim 1, wherein the non-magnetic layer of the memory layerincludes at least one selected from the group consisting of Cu, Ag, Au,V, Ta, Zr, Nb, Hf, W, Mo, and Cr.
 4. The memory device according toclaim 1, wherein the magnetization-fixed layer has a fixed magnetizationperpendicular to the film face and parallel to the thickness directionof the memory device.
 5. The memory device according to claim 1, whereinthe non-magnetic oxide layer includes at least one selected from thegroup consisting of silicon oxide, magnesium oxide, tantalum oxide,aluminum oxide, cobalt oxide, zirconium oxide, titanium oxide, andchromium oxide.
 6. The memory device according to claim 1, wherein thefirst and second ferromagnetic material layers include a composition ofCo, Fe, and B.
 7. The memory device according to claim 1, wherein athickness of the non-magnetic layer is equal to a thickness of thenon-magnetic oxide layer.
 8. The memory device according to claim 1,wherein the first and second ferromagnetic material layers have a samethickness.
 9. The memory device according to claim 1, wherein the memorylayer further comprises a third ferromagnetic material layer, a secondnon-magnetic layer, and a second non-magnetic oxide layer, the secondnon-magnetic layer and the second non-magnetic oxide layer between thethird ferromagnetic material layer and the first or second ferromagneticmaterial layer.
 10. The memory device according to claim 9, wherein thesecond non-magnetic layer is in direct contact with the first or secondferromagnetic material layer and the second non-magnetic oxide layer isin direct contact with the third ferromagnetic material layer.
 11. Thememory device according to claim 9, wherein the second non-magneticoxide layer is in direct contact with the third ferromagnetic materiallayer.
 12. A memory device, comprising: a first magnetization layerincluding a plurality of ferromagnetic material layers, a non-magneticlayer, and a non-magnetic oxide layer; a second magnetization layerincluding a magnetic layer with a fixed magnetization direction; and anintermediate layer between the first magnetization layer and the secondmagnetization layer, wherein, the plurality of ferromagnetic materiallayers include a first ferromagnetic material layer and a secondferromagnetic material layer, the non-magnetic layer is in directcontact with the first ferromagnetic material layer and the non-magneticoxide layer is in direct contact with the second ferromagnetic materiallayer, the non-magnetic layer and the non-magnetic oxide layer are indirect contact with each other and are between the first ferromagneticmaterial layer and the second ferromagnetic material layer, the firstmagnetization layer includes a magnetization perpendicular to a filmface of the first magnetization layer and parallel to a thicknessdirection of the memory device, a direction of the magnetization beingchangeable, and wherein a perpendicular direction of the magnetizationof the first magnetization layer is changeable by applying a current inthe thickness direction of the memory device to record information inthe first magnetization layer, the first and second ferromagneticmaterial layers each comprising a same ferromagnetic element and havinga same direction of magnetization.
 13. The memory device according toclaim 12, wherein the non-magnetic layer includes a metallic materiallayer and is not an oxide layer.
 14. The memory device according toclaim 12, wherein the intermediate layer includes magnesium oxide. 15.The memory device according to claim 12, wherein the secondmagnetization layer has a fixed magnetization perpendicular to the filmface and parallel to the thickness direction of the memory device. 16.The memory device according to claim 12, wherein the non-magnetic oxidelayer includes at least one selected from the group consisting ofsilicon oxide, magnesium oxide, tantalum oxide, aluminum oxide, cobaltoxide, zirconium oxide, titanium oxide, and chromium oxide.
 17. Thememory device according to claim 12, wherein at least one of the firstand second ferromagnetic material layers includes a composition of Co,Fe, and B.
 18. The memory device according to claim 12, wherein athickness of the second magnetization layer is larger than a thicknessof the first magnetization layer.
 19. The memory device according toclaim 12, wherein the second magnetization layer includes a Ru layer.20. The memory device according to claim 19, wherein the secondmagnetization layer further includes a CoPt layer, and wherein the CoPtlayer is in direct contact with the Ru layer.
 21. The memory deviceaccording to claim 20, wherein a thickness of the CoPt layer is largerthan the Ru layer.
 22. The memory device according to claim 12, whereinthe memory device further includes an underlying layer, and wherein theunderlying layer further includes a Ta layer.